I checked the SSL setting of my server. The result was "A +". I will enumerate points devised by setting.
/etc/apache2/sites-enabled/default-ssl.conf
Header always set Strict-Transport-Security "max-age=63072000; includeSubDomains"
SSLProtocol ALL -TLSv1 -SSLv2 -SSLv3
SSLHonorCipherOrder on
SSLCipherSuite HIGH:MEDIUM:!aNULL:!MD5:!RC4:!DES:!DH:
